Pollution: concentration and presence of metals in river sediments in China

In China, there are more than 50,000 rivers with their own catchment areas exceeding 100 km²

by Lorenzo Ciotti
Pollution: concentration and presence of metals in river sediments in China

In China, there are more than 50,000 rivers with their own catchment areas exceeding 100 km². Of those that have waters at any time of the year, about 95% flows directly into the sea (more than 80% in the Pacific Ocean, 12% in the Indian Ocean, and less than 1% in the Arctic Ocean.

) and 5% disperses its waters inland. The three main rivers of China, each of which generally flow from west to east, flowing into the China Sea, are the Huang He, the Yangtze and the Xi Jiang. Huang He, which originates from the Kunlun Mountains, is the northernmost of the three; it flows into the Bo Hai (Gulf of Chihli), north of the Shandong peninsula.

The Yangtze, the longest river in the country, originates in the Tibetan highlands and flows through central China, flowing into the East China Sea north of Shanghai. The Xi River, the southernmost of the three, originates on the Yunnan-Guizhou Plateau and flows into the South China Sea via the Pearl River Delta in Guangzhou (Canton).

The distribution of surface waters in China is extremely uneven. Only a small part of the country has enough water for the whole year. Much of the country receives heavy rainfall, but only during the rainy season when there is surplus water.

From south-east to north-west, the surface waters decrease as the relief becomes more mountainous. In a large area of ​​the north-west there is no water all year round. Northern China (north of the Qin-Huai River line), with its flat relief and long agricultural tradition, owns nearly two-thirds of China's cultivated land; paradoxically, due to the scarce and irregular rainfall, the average annual runoff from the North is just one sixth of the total of that of the whole of China.

The study: Concentrations, Distribution, and Pollution Assessment of Metals in River Sediments in China, published on the International journal of environmental research and public health, said: "This study conducted a review on the concentrations, spatial distribution and pollution assessment of metals including As, Hg, Cd, Co, Cr, Cu, Mn, Ni, Pb and Zn in 102 river sediments in China between January 2008 and July 2020 based on the online literature.

The geo-accumulation index (Igeo) and potential ecological risk index (RI) were used for the pollution assessment of the metals. The results showed that the ranges of metals were: 0.44 to 250.73 mg / kg for As, 0.02 to 8.67 mg / kg for Hg, 0.06 to 40 mg / kg for Cd, 0.81 to 251.58 mg / kg for Co, 4.69 to 460 mg / kg for Cr, 2.13 to 520.42 mg / kg for Cu, 39.76 to 1884 mg / kg for Mn, 1.91 to 203.11 mg / kg for Ni, 1.44 to 1434.25 mg / kg for Pb and 12.76 to 1737.35 mg / kg for Zn, respectively.

The median values ​​of these metals were descending in the order: Mn> Zn> Cr> Cu> Pb> Ni> Co> As> Cd> Hg. Compared with the SQGs, As and Cr manifested higher exceeding sites among the metals.

Metals of river sediments manifested a significant spatial variation among different regions, which might be attributed to the natural weathering and anthropogenic activity. The mean Igeo values ​​of the metals presented the decreasing trends in the order: Cd> Hg> Zn> Cu> As> Pb> Ni> Co> Cr> Mn.

Cd and Hg manifested higher proportions of contaminated sites and contributed most to the RI, which should be listed as priority control of pollutants. Southwest River Basin, Liaohe River Basin, and Huaihe River Basin manifested higher ecological risks than other basins.

The study could provide a comprehensive understanding of metals pollution in river sediments in China, and a reference of the control of pollutant discharge in the river basins for the management."